Add documentation

README.md

doc/images/connect_psql_bash.png.png

tp_jpa/.classpath

tp_jpa/.gitignore

tp_jpa/.gradle/3.5/taskHistory/fileHashes.bin

tp_jpa/.gradle/3.5/taskHistory/taskHistory.lock

tp_jpa/build.gradle

tp_jpa/src/main/java/Library.java

tp_jpa/src/main/java/hello/Economic.java

tp_jpa/src/main/java/hello/EconomicRepository.java

tp_jpa/src/main/java/hello/SampleController.java

.../main/java/org/mines/douai/j2ee/tp/delahaye/Economic.java

.../org/mines/douai/j2ee/tp/delahaye/EconomicController.java

.../org/mines/douai/j2ee/tp/delahaye/EconomicRepository.java

.../src/main/java/org/mines/douai/j2ee/tp/delahaye/Test.java

tp_jpa/src/main/resources/META-INF/persistence.xml

tp_jpa/src/main/resources/application.properties

tp_jpa/src/test/java/LibraryTest.java